The skin is an anatomical and physiological boundary critical to the survival of an individual. The skin is composed of two layers, the dermis and the epidermis. The dermis is a deeper layer of the skin giving the skin mechanical strength. In contrast, the epidermis is superficial and is the body's primary barrier to the environment. Multiple superficial lesions may develop in the epidermis. These lesions are usually removed by common, outpatient procedures.
Examples of very common epidermal lesions include verruca vulgaris (warts), actinic keratosis (precancerous lesions on the skin), and seborrheic keratosis (benign overgrowths). Less common but still significant lesions include basal cell carcinomas, squamous cell carcinomas, and malignant melanoma. Most epidermal lesions form through neoplasia (cancers) or hyperplasia (overgrowth of normal cells).
Typical treatments for epidermal lesions are based on excision, destruction and immunomodulation (modifying the immune system to cause self elimination). Excision is the removal by cutting. Destruction may be accomplished through liquid nitrogen therapy (freezing), curettage (a form of scraping the lesion off), electrodessication (essentially burning the lesion with an apparatus that creates a spark), and lasers (causing vaporization of the lesion). Immunomodulation is accomplished by using chemicals such as 5-fluorouracil, imiquimod, tretinoin, etc., to create or modify an immune response to treat specific lesions.
All of the treatment modalities have the risk of pain, bleeding, infection, recurrence, and scarring. The decision as to which treatment to use is based on the nature of the lesion (benign or malignant), the number of lesions, the location of the lesion, the age of the patient, and co-morbid conditions in the patient.
In particular, liquid nitrogen is a common method of destruction as it is easy to perform on an outpatient basis and is usually effective. The specialties that use the procedure the most include dermatologists, pediatricians, family practitioners, and internists. The main complication or common side effects of liquid nitrogen therapy include pain associated with the procedure, blistering, swelling, ulceration, discoloration, infection, and scarring.
These types of discomfort can cause significant psychological distress in patients, particularly children. Typically, liquid nitrogen therapy causes two types of pain: one, an immediate pain associated with the freezing process of the skin; and two, a delayed pain that occurs during and after the thaw cycle. The post-thawing pain frequently is the most painful and can last for hours.
One of the benefits of liquid nitrogen therapy is that it can be used on the general population. The limitations of the therapy are that it is difficult to judge the depth of the freezing necessary, and that there is pain associated with the therapy. There may be some limits to the size of lesions that can be frozen, but as of yet, there are no established guidelines in that regard.
In order to ameliorate the pain associated with liquid nitrogen therapy, topical anesthetics are used. These topical anesthetics may contain, but are not limited to, lidocaine, eutectic mixtures of lidocaine and prilocaine, liposomal lidocaine, and lidocaine with AcidMantle® vehicle. The recommended and manufacturer directed use of these anesthetics is local application with or without occlusion 30-60 minutes prior to any procedure to achieve any anesthetic effect.
The use of topical anesthetics prior to the use of liquid nitrogen, however, has limited efficacy in relieving pain. This is due in part to the hyperkeratotic nature of the lesions treated. Hyperkeratotic lesions have a thickened stratum corneum (the tough, impermeable, outermost layer of the epidermis). An example of this type of lesion is a wart. This thickness likely prevents the diffusion of any anesthetic from the surface of the skin into the deeper layers where it would exert its effect.
What is needed therefore is a method of using liquid nitrogen therapy that diminishes the amount of pain that a patient may incur with the treatment of an epidermal or cutaneous lesion by liquid nitrogen. In particular, a method is needed to reduce or diminish the pain a patient experiences during and after the thawing cycle of the liquid nitrogen therapy.
It is therefore an advantage of some, but not necessarily all, embodiments of the present invention to provide a novel method for the relief of pain associated with the use of liquid nitrogen for the treatment of epidermal or cutaneous lesions.
In particular, none of the above-mentioned approaches recognize the extent of pain following the thawing cycle of liquid nitrogen therapy as illuminated in the present invention, which is briefly outlined in the following Summary of the Invention, and more fully described in the Detailed Description.
Additional advantages of various embodiments of the invention are set forth, in part, in the description that follows and, in part, will be apparent to one of ordinary skill in the art from the description and/or from the practice of the invention.